The KP04 is a keypad which primarily operates the Alarm system, to allow you to arm and disarm the security. It also has many advanced features like being able to record and play messages as well as intercom with the Door Station.
When someone presses the doorbell on the Door Station, the phones in the home
will ring and the keypad will chime. You can use the phone or the keypad to talk to the visitor and open the door or gate if the appropriate interfacing is done